Create README.md

Author: StuartIanNaylor

swap-performance/README.md

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+# Swap-performance
+Using a raspbian lite / zram-config and https://github.com/StuartIanNaylor/MagicMirror-Install-Guide-Raspberry-0-to-3
+with mirrorcomplex and plymouth pretty.
+
+15 min boots logging /proc/loadavg every 2 secs stored in a spreadsheet with the average of 3 datasets looking at:-
+1st 30 seconds
+1st Minute
+1st 2 minutes
+Overall load
+Last 2 minutes
+Last minute
+
+
+
+_____
+
+### Performance
+LZO/4 offer the best performance and for swaps they are probably the defacto choice.
+You maybe have text based low impact directories such a /var/log /var/cache where highly
+effective text compressors, such as deflate(zlib) & zstd are used in preference of disk size
+and effective compression that can be up to 200% of what a LZ may achieve.
+/tmp I am not so sure about incur any further load on what can be small blistering fast
+ram mounted tmpfs as if memory gets short then zram swaps will provide.
+That way your system is performance optimised and also memory optimised via zram swap,
+with compression overhead of some common working directories.
+The choice is yours though and its very dependent on the loading you commonly run with.
+Its only at intense load the slight overhead of zram compression becomes noticeable.
+A Pi-Zero obviously shows far more effect than a Pi-3B+
+LZO-RLE has roled out in the latest kernels and is the new default for zram and still don't
+know if that will change my own personal pick of LZ4.
+Until I can find another comparative benchmark that includes all this list is a good yardstick.
+
+| Compressor name	     | Ratio	| Compression | Decompress. |
+|------------------------|----------|-------------|-------------|
+|zstd 1.3.4 -1	         | 2.877	| 470 MB/s	  | 1380 MB/s   |
+|zlib 1.2.11 -1	         | 2.743    | 110 MB/s    | 400 MB/s    |
+|brotli 1.0.2 -0	     | 2.701	| 410 MB/s	  | 430 MB/s    |
+|quicklz 1.5.0 -1	     | 2.238	| 550 MB/s	  | 710 MB/s    |
+|lzo1x 2.09 -1	         | 2.108	| 650 MB/s	  | 830 MB/s    |
+|lz4 1.8.1	             | 2.101    | 750 MB/s    | 3700 MB/s   |
+|snappy 1.1.4	         | 2.091	| 530 MB/s	  | 1800 MB/s   |
+|lzf 3.6 -1	             | 2.077	| 400 MB/s	  | 860 MB/s    |
+
+With Swaps Zram changes what are static assumptions of HHD providing swaps in terms of swapiness
+and page-cache where default swapiness is 60 and page-cache is 3 to buffer page-writes of 8.
+Employing near memory based swaps needs tuning for near memory based swaps and the current defaults
+are far from optimised.
+Depending on avg load Zram will benefit from a setting of 80 -100 and changing page-cache to 0 so that
+singular pages are written will greatly reduce latency.
+Its a shame swapiness is not dynamically based on load as for many systems there is often a huge difference
+in boot startup to settled load.
+In some cases you may find you are reducing swapiness purely because of boot load.